The demand for services in which data is delivered via a wireless connection has grown in recent years and is expected to continue to grow. Included are applications in which data is delivered via cellular mobile telephony or other mobile telephony, personal communications systems (PCS) and digital or high definition television (HDTV). Though the demand for these services is growing, the channel bandwidth over which the data may be delivered is limited. Therefore, it is desirable to deliver data at high speeds over this limited bandwidth in an efficient, as well as cost effective, manner.
A known approach for efficiently delivering high speed data over a channel is by using Orthogonal Frequency Division Multiplexing (OFDM). The high-speed data signals are divided into tens or hundreds of lower speed signals that are transmitted in parallel over respective frequencies within a radio frequency (RF) signal that are known as sub-carrier frequencies (“sub-carriers”). The frequency spectra of the sub-carriers overlap so that the spacing between them is minimized. The sub-carriers are also orthogonal to each other so that they are statistically independent and do not create crosstalk or otherwise interfere with each other. As a result, the channel bandwidth is used much more efficiently than in conventional single carrier transmission schemes such as AM/FM (amplitude or frequency modulation).
Another approach to providing more efficient use of the channel bandwidth is to transmit the data using a base station having multiple antennas and then receive the transmitted data using a remote station having multiple receiving antennas, referred to as Multiple Input-Multiple Output (MIMO). The data may be transmitted such that there is spatial diversity between the signals transmitted by the respective antennas, thereby increasing the data capacity by increasing the number of antennas. Alternatively, the data is transmitted such that there is temporal diversity between the signals transmitted by the respective antennas, thereby reducing signal fading.
In wireless communication systems, control signals are used to pass information between sender and receiver for allowing the transmission of data therebetween. Control signals are not part of the transmission data being sent between users, but rather serve to coordinate communications between the sending and receiving devices, and otherwise to enable and facilitate communication. Generally, control signals are relatively important to communications, and they are usually transmitted in a more robust fashion than other data. While reliability of transmission of control signals is usually important, control signals are often quite small, despite their important role.
It is a basic objective in wireless systems to reliably transmit small quantities of information such as are found in control signals in a manner that function for all user scenarios. This represents a particular challenge in new standards such as IEEE802.16m, which aim to provide even more flexible deployment environment and support a variety of channel conditions, mobile speeds and other factors.
In IEEE802.16m, uplink control signals currently use sub-optimal modulation and coding schemes, in particular for the channel quality information channel (CQICH) and for acknowledgements (ACK). For example, a high overhead is imposed by the use of pilot in manners that have not been shown to be advantageous over other methods.
Accordingly, there is a need for an improved uplink control design for the mobile, broadband wireless access systems.